This invention relates generally to integrated circuit fabrication techniques and, more particularly, to methods for integrating monolithic microwave integrated circuit (MMIC) and micro electromechanical systems (MEMS) components into a single package. MMIC technology necessitates the use of an extremely thin substrate, in the range of 50–100 μm, and a MEMS device necessarily has significant thickness because it is basically a three-dimensional device. Moreover, MEMS devices cannot operate reliably in the field without hermetic packaging.
Integration of MEMS devices, such as radio frequency (RF) MEMS switches, with MMIC technology offers significant system performance improvements, such as low loss, high linearity and added functionality, in many space and military applications, especially those operating at very high frequencies, e.g., approaching 500 GHz (gigahertz) and above. There are, however, practical difficulties inherent in combining the two technologies. MMIC components are formed in one face of a very thin substrate and employ conductive vias to make connections through the “back” face of the substrate, while MEMS devices are preferably formed in a three-dimensional, hermetically sealed cavity, which dictates the use of a mechanically sturdy package. Reconciling the needs of MMIC components with those of MEMS components in an integrated package is one important goal of the present invention. A related goal is to achieve cost savings of the type normally associated with wafer-level fabrication and packaging of integrated circuitry, but in this case rendered very difficult to achieve by the thin substrate structure of MMIC components.